Security Scanners

6. Conclusion: are X-ray security scanners safe?

The SCENIHR opinion states:

4. OPINION

This document is prepared in response to the request of the
Commission and provides a summary of the scientific knowledge on
the potential health effects of X-ray based security scanners
for passenger screening. It is not intended to address the issue
of justification, which remains a national prerogative, as
specified in the relevant EU legislative framework for
radiation
protection. This framework specifies the requirements for use of
all equipment using ionising radiation, including prior
justification before a practice is introduced.

The justification for introducing a new practice, particularly
outside the medical field, is a complex process and
radiation
protection considerations are only one aspect. In the use of
X-ray security scanners for screening individuals, the benefit
accrues primarily to society rather than to the exposed
individual. The risk-benefit ratio should be considered in the
justification prior to a practice being introduced but this may
also need to be revisited when new technologies are introduced
or new information becomes available.

Although the doses per scan arising from the use of screening
for security purposes are well below the public dose limit, this
does not remove the requirement for justification. In addition,
for practices that are justified and subsequently authorised,
optimisation measures must be taken so that all exposures are as
low as reasonably achievable (the ALARA principle) for workers,
the general public, and the population as a whole.

The SCENIHR was asked:

1. To assess the potential health effects related to the use
of all types of security scanners used for passenger
screening which emit ionising
radiation.

Although the radiation doses from a single scan are in the
range of nano- to microsievert, those from transmission scanners
are at least 10 times higher than those from backscatter
scanners. This difference could result in significantly higher
cumulative doses which may exceed the annual dose limit for
members of the public if transmission scanners are used as
routine screening devices for frequently exposed individuals
(airline crews, frequent flyers, airport personnel, etc.). The
higher doses used by transmission scanners must be given an
emphasis in the justification process.

2. If any effects are identified under 1, to quantify the
risks and, if feasible, to estimate the additional number of
cases of diseases that are expected to occur in Europe due
to the use of this technology at EU airports,
differentiating between the general public and exposed
workers as indicated below.

The dose levels from the use of security scanners are well
below the range where any health effects are observable. Due to
the very low radiation doses to both scanned passengers and the
exposed workers, any quantitative estimation of risk would be
highly uncertain and rely on non verifiable assumptions about
extrapolations to dose levels where health effects cannot be
demonstrated. The risk assessment performed here relies on the
linear no-threshold model according to which the probability of
adverse effects is directly proportional to the
radiation dose.
The risk estimates are based on theoretical projections from
observations at substantially higher exposure levels. There is
no sufficient scientific basis for making any quantitative risk
estimates such as calculating the additional number of
cancer cases
induced by the introduction of security scanners at airports,
either to the general public or the exposed workers.

In its assessment, the SCENIHR is asked to consider in
particular the risk for populations that are regularly
exposed to such technologies (e.g. frequent flyers (to be
defined), air crew, security workers operating the scanners
and other airport staff) and potentially vulnerable groups
(e.g. pregnant women, children).

All those screened including frequent flyers and airline crews
are subject to the public dose limit of 1 millisievert per year.
Annual cumulative effective doses would remain below that level
for backscatter technology even with highest plausible scan
frequencies (three scans every working day of the year), but
with transmission technology such a dose limit could be exceeded
for individuals with such high scan frequency. Appropriate dose
constraints for members of the public should be set at a
substantially lower level than the public dose limit. While a
suitable constraint would be very unlikely to be approached for
most passengers who are scanned using backscatter scanners, it
could potentially be exceeded by those persons who are scanned
several times a day throughout the year (e.g. flight crew,
ground staff). It would be appropriate to apply a higher
constraint value to these groups. However, even in this scenario
the annual dose limit for members of the public would not be
approached or exceeded. By contrast, the scanning of frequent
fliers with X-ray transmission scanners could result in both the
constraint and dose limit for members of the public being
exceeded.

In view of the low doses from backscatter security scanners
there is no scientific basis to separately consider potentially
vulnerable groups (e.g. pregnant women, children) in risk
assessment. Cumulative doses are very likely to remain below the
constraints with backscatter scanners even for frequently
scanned individuals.

Use of transmission scanners could result in exceeding dose
constraints for frequent flyers and certain occupational groups.
An occasional transmission scan does not require separate
consideration even for potentially vulnerable groups of the
population.

The SCENIHR should compare the relative risk of such
security scanners using X-ray based technologies to other
security scanner technologies on the market.

The current scientific evidence does not allow for a direct
comparison of various technologies because of the different
nature of exposure for ionising and non-ionising
radiation. There is
no scientific basis for predicting stochastic health effects of
passenger scanning technologies using non-ionising radiation
such as mm wave or THz scanners. Furthermore, the thermal
effects of exposure to non-ionising radiation are not cumulative
and non thermal health effects are not proven. The use of these
technologies has been shown to comply with exposure limits based
on thermal effects (ICNRP).

At the levels typical of X-ray based security scanners, only
stochastic effects could occur, but the predicted probability of
their occurrence is very low and there is no scientific evidence
supporting their existence.

Passive devices that do not emit any
radiation are not
expected to have any adverse health effects.